A. Field of the Invention
The present invention relates generally to Anti-Submarine Warfare (ASW), and more particularly, to the detection of submarines using explosions to implement an active sonar system.
B. Description of Related Art
Submarines have been used as military weapons since the 18th century. Early submarines contained only crude weapons and had limited success.
Modern submarines, in contrast, have advanced significantly since the early days of the submarine. To combat modern enemy submarines, the military uses a number of ship and air based techniques to locate and destroy enemy submarines. Anti-submarine warfare (ASW) is a term used to generally describe techniques and devices employed for detecting and neutralizing submarines.
Detecting a submarine can be a difficult proposition: Multiple types of sensors may be used to detect enemy submarines. ASW sensors are divided into two basic types: acoustic and non-acoustic. Each sensor may have specific applications that counters different submarine operations. Many of these sensors complement and corroborate each other to enhance ASW effectiveness.
Non-acoustic sensors augment the detection capability provided by acoustic sensors. These sensors may use radar to detect exposed periscopes and hull surfaces, electro-magnetic systems to intercept the radar emissions from submarines, infra-red receivers to detect the heat signatures of surfaced submarines, or Magnetic Anomaly Detectors (MAD) to sense small changes in the Earth""s magnetic field caused by the passage of a submarine.
Acoustic sensors, on the other hand, are based on the detection of sound waves traveling through the water. One type of acoustic sensor is a hydrophone used for detecting water-borne acoustic signals. Hydrophones may be employed in two general types of ASW systems, namely passive systems or active systems. In a passive ASW system, listening devices such as hydrophones are used to detect sound waves radiating from a submarine. Examples of sounds detected using passive listening techniques are machinery noise, propeller noise, torpedo launching transients, etc. In active ASW systems, a noise is generated and transmitted through the water such that it hits a submarine and is reflected back to a listening device such as a hydrophone. In active detection systems, short high intensity sound pulses are often used to detect submarines in an analogous way that radar signals are used in air to detect objects.
One conventional active acoustic sensing system involves dropping an explosive, typically from a helicopter, into the water. The explosion in the water generates a broadband impulsive event. Sensors, such as hydrophones implemented in a number of sonobuoys distributed around the area of the explosion, record the acoustic signals. Information from the sonobuoys can then be analyzed to locate objects, such as submarines, that are present in the water.
xe2x80x9cSeedingxe2x80x9d the water with explosives dropped from helicopters or planes can be an effective way to locate enemy submarines. However, the helicopter""s load-limits constrain the number of explosives it can deploy per flight. Further, bad weather or operational dangers (such as enemy fire) can further degrade the usefulness of this approach to locating enemy submarines.
Accordingly, it would be desirable to more effectively implement an active sonar system that uses explosives to seed the water without requiring an aircraft.
Systems and methods consistent with the principles of this invention implement a projectile sonar system in which a shell launched via the gun of a ship is used to create an impulsive acoustic signal. The shells may also be used as standard munitions.
One aspect of the invention is directed to a method of detecting an object in a body of water. The method includes firing an explosive shell from a gun on a ship at a target location in the body of water, measuring acoustic signals caused by an explosion of the shell in the water, and identifying objects in the water based on the measured acoustic signals.
A second aspect of the invention is directed to a system that includes logic configured to receive acoustic signals from a sensor. The system additionally includes a feature extractor and a classifier. The feature extractor locates features in the acoustic signals and the classifier classifies the located features as an object. The system further includes a gun control component coupled to an output of the classifier and configured to set a location and depth for firing a shell from a gun of a ship, the shell being used to generate additional acoustic signals for processing by the feature extractor.
Another aspect of the invention is a system that includes a number of elements. In particular, the system includes sonobuoys positioned in a body of water, each of the sonobuoys include a sensor that senses acoustic signals in the body of water and a transmitter that transmits the sensed acoustic signals. The system further includes at least one gun configured to fire shells into the body of water and a first processing component. The first processing component is located on a ship and receives the acoustic signals from the sonobuoys and determines locations of objects in the body of water based on the acoustic signals.
Yet another aspect of the invention is directed to a method. The method includes receiving acoustic signals that correspond to an underwater explosion caused by detonation of a shell fired from a gun of a ship. The method further includes analyzing the acoustic signals to determine locations of underwater objects.